This invention is generally directed to improved layer photoresponsive imaging members, and more specifically the present invention is directed to stabilized layered photoresponsive devices comprised of electron transporting layers having incorporated therein stabilizing compositions. In one specific embodiment of the present invention there is provided a photoresponsive imaging member or device comprised of an electron transporting layer having incorporated therein stabilizing compositions, including various diamine molecules, and a photogenerating layer. Also, in accordance with the present invention there is provided a process for affecting the stabilization of electron transporting compositions by incorporating therein various stabilizing compositions, including specific diamine molecules as illustrated herein, hydrazone compositions and other similar electron donating substances. The improved photoresponsive devices of the present invention are particularly useful in electrostatic imaging systems wherein, for example, the device is initially charged positively.
The formation and development of electrostatic latent images on surfaces of photoconductive materials by electrostatic means is well known, one such method involving the formation of an electrostatic latent image on the surface of a photoreceptor. This photoreceptor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material, and in many instances a thin barrier layer is situated between the substrate and the photoconductive layer to prevent charge injection from the substrate, as injection could adversely affect the quality of the images generated.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material, such as vitreous selenium; or a composite layered device with a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described in U.S. Pat. No. 3,121,006 wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resinous binder. In a commercial form the binder layer contains particles of zinc oxide uniformly dispersed in a resinous binder, and coated on a paper backing. The binder material as disclosed in this patent comprises a composition which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Illustrative examples of specific binder materials disclosed include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor materials comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layerof an electrically insulating polymeric material. However, the art of exerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain high quality images. Additionally, photoresponsive devices are desired which can be charged positively, and contain therein an electron transporting material.
Recently, there has been disclosed layered photoresponsive devices comprised of photogenerating layers and transport layers, as described in U.S. Pat. No. 4,265,990; and overcoated photoresponsive materials containing a hole injecting layer in contact with a transport layer, an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, reference, for example, U.S. Pat. No. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium, and phthalocyanines, while examples of transport layers that may be used, which layers transport positive charges, in contrast to the transport layers of the present invention which transport electrons include certain diamines dispersed in a resinous binder. The disclosure of each of these patents, namely U.S. Pat. Nos. 4,265,990 and 4,251,612 are totally incorporated herein by reference.
Many other patents are in existence describing photoresponsive devices including layered devices with generating substances, such as U.S. Pat. No. 3,041,167. This patent discloses an overcoated imaging member with a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in electrophotographic copying by, for example, initially charging the member with electrostatic charges of a first polarity, and imagewise exposing to form an electrostatic latent image, which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity, which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer by applying an electrical potential to the conductive substrate. The imaging potential, which is developed to form the visible image, is present across the photoconductive layer, and the overcoating layer.
Furthermore, there is disclosed in U.S. Pat. No. 4,135,928 electrophotographic light sensitive members with 7-nitro-2-aza-9-fluorenylidenemalononitrile as a charge transporting substance. According to the disclosure of this patent, the electrophotographic light sensitive members comprise an electroconductive support, a layer thereof comprising a charge generating substance, and 7-nitro-2-aza-9-fluorenylidene-malononitrile, of the formula, for example, as illustrated in column 1.
Other representative patents disclosing layered photoresponsive devices include U.S. Pat. Nos. 4,115,116, 4,047,949, and 4,315,981. There is disclosed in the '981 patent an electrophotographic recording member with an organic double layer. According to the disclosure of this patent, the recording member consists of an electroconductive support material and a photoconductive layer of organic maerials, which contain a charge carrier producing dyestuff layer of a compound having an aromatic or heterocyclic polynuclear quinone ring system, and a transparent top layer of certain oxdiazoles. Apparently, this recording member is useful in electrophotographic copying processes where negative charging of the top layer occurs when an electron donating compound is selected for the device involved.
Moreover, disclosed in U.S. Pat. No. 4,442,192 entitled Improved Photoresponsive Device Containing an Electron Donating Layer, are photoresponsive devices comprised of a photoconductive composition layer, a trapping layer, and an overcoating layer containing a material capable of donating electrons. More specifically, there is disclosed in this an improved layered photoresponsive device with a conductive substrate, a photogenerating layer, a trapping layer for retaining positive charges at the interface between the overcoating layer and the trapping layer, which layer also prevents these charges from migrating into the photogenerating layer, and an overcoating layer comprised of a material capable of donating or transferring electrons to positive charges contained on the surface of the photoresponsive device, which overcoating layer consists of N,N'-diphenyl-N,N'-bis(alkylphenyl)-[1,1-biphenyl]-4,4'-diamines.
Additionally, there is disclosed in copending application U.S. Ser. No. 521,198, entitled Layered Photoresponsive Device, an imaging member comprised of a photogenerating layer, and in contact therewith an electron transporting layer comprised of fluorenylidene derivatives. The disclosure of this copending application is totally incorporated herein by reference.
While the above described photoresponsive imaging members or devices are suitable for their intended purposes, there continues to be a need for other imaging members, particularly layered imaging members. Additionally, there is a need for layered photoresponsive imaging members wherein the electron transporting materials are stabilized with specific aryl amines so as to prevent crystallization of the electron transporting molecules. Moreover, there continues to be a need for improved layered imaging members with stabilized aryl amine electron transporting layers enabling these members to be positively charged. Moreover, there continues to be a need for improved photoresponsive imaging member which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow their continuous use in repetitive imaging and printing systems. Additionally, there continues to be a need for processes for the stabilization of electron transporting molecules by adding thereto various aryl amine stabilizing substances, as illustrated hereinafter.